This invention relates generally to systems for measuring electrical signals form electronic or optoelectronic devices and systems, and more particularly, to an electrode structure having a contact electrode for receiving the signals to be measured, and interdigitated electrode structure forming a metal-semiconductor-metal photoconductive gate, and an output electrode.
There is a need for an arrangement which can communicate directly with one or more portions of a circuit to be tested, such as an integrated circuit, and particularly for facilitating internal node testing within very large scale integration (VLSI) systems. Such node testing requires compliance with increasingly challenging specifications, since VLSI systems are increasing in circuit component density, and soon will have electrode dimensions nearing 0.1 .mu.m. Additionally, such VLSI systems will soon be operating a very high speeds, on the order of 50 ps and below. Known measurement systems fall short, by at least an order of magnitude of reaching both of these benchmarks simultaneously.
In addition to achieving communication with specific nodes within a VLSI system, and achieving the high gate speeds necessary to achieve meaningful measurements, it is essential that the measuring system be nondisturbing, in several senses. First, the measurement system should have a high electrical impedance so as not to produce loading of the integrated circuit components. Such electrical loading not only disturbs the circuit under test whereby the results obtained are representative of the operation of the circuit, but also present a danger to the circuit under test since such high density systems operate at extremely small currents. In addition, it is crucial that the measurement system not disturb the integrated circuit mechanically. It is well known that the internal mechanical structures of integrated circuits, particularly VLSI systems are extremely small and fragile.
A system for measuring signals in integrated circuitry should, in addition to the foregoing, produce absolute voltage measurements, including DC-offsets. In this manner, a true representation of the electrical activity within the integrated circuit is achieved. Such measurements should additionally be free of cross-talk from adjacent electrode structures.
With respect to temperature, there is a need for a system which can function at ambient temperatures and pressures which are elevated and fluctuating. Oftentimes, elevation in temperature is produced by the circuit under test, and therefore, it is imperative that the measurements system not itself be responsive to such temperatures.
Prior art arrangements have been unable to achieve a sufficient sensitivity. Such sensitivity preferably should be on the order of 1 .mu.V/.sqroot.Hz at a 1 MHz repetition rate. In addition, the measurement system should be translatable over a field of view of the circuit under test of at least 500 .mu.m by 500 .mu.m.
Currently available measurement systems are not capable of probing bonded pads and through-holes in passivation layers. Neither is there available in the state of the art a system capable of probing intermediate circuit layers of multilayer circuits.
It is, therefore, an object of this invention to provide temporal resolution of less than 50 ps, and preferably on the order of 1 ps.
It is another object of this invention to provide a measurement system which achieves a spatial resolution of 0.1 .mu.M with repeat positionability.
It is also an object of this invention to provide an arrangement capable of measuring signals in VLSI circuits which does not disturb the circuit electrically.
It is a further object of this invention to provide a system for measuring signals in integrated circuits which does not disturb the circuit under test mechanically.
It is additionally an object of this invention to provide a system for measuring signals in integrated circuits which is immune to cross-talk from adjacent electrode structures.
It is yet a further object of this invention to provide a system which provides repeatable measurements of signals in VLSI circuits and which is immune to variations in ambient temperature and pressure.
It is also another object of this invention to provide a signal measurement system which achieves sensitivity on the order of 1 .mu.V/.sqroot.Hz at 1 MHz repetition rate.
It is yet an additional object of this invention to provide an integrated circuit measurement and testing arrangement which can test over a field of view of at least 500 .mu.m by 500 .mu.m.
It is still another object of this invention to provide a system for measuring signals in integrated circuits which is capable of probing bonded pads and through-holes in passivation layers.
It is a yet further object of this invention to provide an integrated circuit measurement system which is capable of probing intermediate circuit layers.
It is also a further object of this invention to provide a system for measuring signals in integrated circuits which is capable of multiple, synchronous measurements.
It is additionally another object of this invention to provide an arrangement for producing controlled translation of a probe over a VLSI system for communicating with predetermined portions of the VLSI system.
A still further object of this invention is to provide a system which achieves pulser and sampler functions using a single probe tip.
An additional object of this invention is to provide a system which achieves sampling at frequencies greater than 100 MHz.
Yet another object of this invention is to provide a system which achieves pulsing at frequencies greater than 100 MHz.